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You are watching: Are the spores produced by the moss sporophyte formed by meiosis or mitosis

Gilbert SF. Developmental Biology. Sixth edition. Sunderland (MA): Sinauer Associates; 2000.

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The plant life cycle alternates in between haploid and also diploid generations. Embryonic advance is seen only in the diploid generation. The embryo, however, is created by the blend of gametes, i m sorry are created only by the haploid generation. So understanding the relationship between the 2 generations is crucial in the research of plant development.

Unlike animals(see chapter 2), plants have actually multicellular haploid and multicellular diploid step in your life cycle. Gametes construct in the multicellular haploid gametophyte (from the Greek phyton, “plant”). Fertilization provides rise to a multicellular diploid sporophyte, i beg your pardon produces haploid spores via meiosis. This form of life bike is dubbed a haplodiplontic life bike (Figure 20.1). It differs from our own diplontic life cycle, in which only the gametes space in the haploid state. In haplodiplontic life cycles, gametes space not the direct an outcome of a meiotic division. Diploid sporophyte cells undergo meiosis to produce haploid spores. Every spore goes with mitotic divisions to yield a multicellular, haploid gametophyte. Mitotic divisions within the gametophyte are compelled to develop the gametes. The diploid sporophyte results from the blend of two gametes. Among the Plantae, the gametophytes and sporophytes that a species have unique morphologies (in some algae they look alike). How a single genome have the right to be supplied to develop two distinctive morphologies is an attractive puzzle.


Figure 20.1

Plants have haplodiplontic life cycles that involve mitotic divisions (resulting in multicellularity) in both the haploid and diploid generations (paths A and D). Most animals are diplontic and undergo mitosis just in the diploid generation (paths B and (more...)

All plants alternate generations. There is an evolutionary tendency from sporophytes that space nutritionally dependence on autotrophic (self-feeding) gametophytes come the opposite‐gametophytes that room dependent top top autotrophic sporophytes. This tendency is exemplified by compare the life cycles the a moss, a fern, and an angiosperm (see numbers 20.2– 20.4). (Gymnosperm life cycles bear plenty of similarities to those of angiosperms; the distinctions will be explored in the paper definition of angiosperm development.)


Figure 20.2

Life bike of a moss (genus Polytrichum). The sporophyte generation is dependent on the photosynthetic gametophyte for nutrition. Cells within the sporangium the the sporophyte experience meiosis to create male and also female spores, respectively. This spores (more...)


Figure 20.4

Life bike of an angiosperm, represented here by a pea tree (genus Pisum). The sporophyte is the leading generation, but multicellular male and also female gametophytes are produced within the flowers of the sporophyte. Cells of the microsporangium within (more...)

The “leafy” moss girlfriend walk on in the woods is the gametophyte generation of that plant (Figure 20.2). Mosses are heterosporous, which means they make two distinct species of spores; these construct into male and also female gametophytes. Male gametophytes develop reproductive structures called antheridia (singular, antheridium) that create sperm through mitosis. Woman gametophytes construct archegonia (singular, archegonium) that produce eggs by mitosis. Sperm travel to a surrounding plant via a water droplet, space chemically attracted to the entrance of the archegonium, and fertilization results.* The embryonic sporophyte establishes within the archegonium, and the mature sporophyte continues to be attached to the gametophyte. The sporophyte is no photosynthetic. For this reason both the embryo and also the maturation sporophyte space nourished by the gametophyte. Meiosis in ~ the capsule the the sporophyte returns haploid spores that are released and also eventually germinate to form a male or female gametophyte.

Ferns follow a pattern of development similar to the of mosses, although many (but no all) ferns space homosporous. That is, the sporophyte produces just one type of spore in ~ a structure called the sporangium (Figure 20.3). One gametophyte can create both male and female sex organs. The greatest contrast in between the mosses and the ferns is that both the gametophyte and the sporophyte of the fern photosynthesize and are for this reason autotrophic; the transition to a leading sporophyte generation is acquisition place.†


Figure 20.3

Life bike of a fern (genus Polypodium). The sporophyte generation is photosynthetic and also is independent of the gametophyte. The sporangia are defended by a great of cells referred to as the indusium. This entire structure is referred to as a sorus. Meiosis in ~ the (more...)

At first glance, angiosperms may show up to have a diplontic life cycle because the gametophyte generation has actually been reduced to simply a couple of cells (Figure 20.4). However, mitotic department still complies with meiosis in the sporophyte, bring about a multicellular gametophyte, i m sorry produces egg or sperm. Every one of this takes place in the the body organ that characterizes the angiosperms: the flower. Male and also female gametophytes have distinct morphologies (i.e., angiosperms space heterosporous), yet the gametes they create no longer rely on water because that fertilization. Rather, wind or members the the pet kingdom deliver the masculine gametophyte—pollen—to the woman gametophyte. One more evolutionary invention is the production of a particle coat, which adds an extra layer of protection approximately the embryo. The particle coat is likewise found in the gymnosperms. A further protective layer, the fruit, is distinct to the angiosperms and aids in the dispersal of the enclosed embryos by wind or animals.

The remainder that this chapter gives a comprehensive exploration that angiosperm breakthrough from fertilization to senescence. Save in mind that the an easy haplodiplontic life cycle viewed in the mosses and ferns is additionally found in the angiosperms, continuing the trend toward raised nourishment and also protection of the embryo.

Have you ever wondered why there room no moss trees? aside from the truth that the gametophytes the mosses (and various other plants) execute not have the vital structural support and transport solution to achieve tree height, it would be very an overwhelming for a sperm to swim increase a tree!

It is possible to have actually tree ferns, for 2 reasons. First, the gametophyte establishes on the ground, wherein water deserve to facilitate fertilization. Secondly, unlike mosses, the fern sporophyte has vascular tissue, which provides the support and also transport system necessary to achieve substantial height.

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